The present invention relates to an apparatus for generating pulses at a rate limited in accordance with an analog signal.
In particular, the pulse rate controller of the present invention has been found to be useful in scalloping suppression systems and methods such as disclosed in my above-identified U.S. Pat. No. 4,014,125, incorporated herein by reference.
The scalloping suppression system is used in a V.H.F. Omni Range (VOR) aircraft bearing system. A VOR system is sensitive to differences in phase of a received radial transmission, at typically 30 Hz., in relation to an omni directional transmission, also at 30 Hz. but out of phase with the radial transmission by an amount depending on bearing. The scalloping suppression system is arranged to respond to changes in phase which are due to position changes of the aircraft but not to respond to the generally more rapid changes in phase which are due to scalloping.
In the scalloping suppression system, a digital phase shifter-comparator network is employed to cause the phase of a reference signal to follow the phase of the received radial signal. The phase shifter includes two counters, and the phase comparator can include a bistable multivibrator. The output of the system is a delayed reference signal. An analog rate controller limits the rate at which the reference signal can follow the received radial signal. The limiting is made to be proportional to the distance between the aircraft and the VOR ground station so that the rate of change cannot exceed the phase change due to the velocity of the aircraft orthogonal to the received radial.
The analog rate controller inhibits pulses tending to change the reference signal stored in the phase shifter to an analog voltage level which is applied thereto, which voltage level is indicative of the distance between the aircraft and the ground station. The voltage level is applied to a comparator along with the voltage on a capacitor which is charged from a constant current source. When the capacitor voltage reaches the analog distance voltage, the comparator generates an output, and during the time that it takes the capacitor to charge to the distance voltage pulses tending to change the phase of the system output signal are inhibited.